The present invention relates to the manufacture of bags in general, and more particularly to a method of and arrangement for manufacturing paper bags, especially flat and lateral fold bags for mailing.
There are already known various methods of and arrangements for manufacturing paper bags of the type here under consideration, among them such in which a tube is being shaped from a paper web withdrawn from a roll while simultaneously forming a longitudinal seam. Then, individual tubular pieces are separated from the tube in such a manner that the transverse end edges that are associated with one another and that are constituted on the circumferential panels of the bag extend parallel to one another and at a distance from each other. Finally, the leading ends of the tubular pieces are folded and closed for the formation of the respective bags.
The bags which are being manufactured in accordance with both the conventional methods and arrangements and those of the present invention are to be used for the packaging of various goods or items. Depending on their configuration, the respective bags may be classified as flat bags, lateral fold bags and amiling envelopes. Many modifications or these bag types may be contemplated.
Ordinarily, for the manufacture of the bags, individual tubular sections are separated from a tube that is shaped from a web. Usually, the shaping of the tube is accomplished in such a manner that the outer regions of the web are folded over toward the center such that the longitudinal marginal portions of the web overlap one another and form a so-called longitudinal seam. To the extent that the material of the bag is capable of being adhesively connected, such as paper, the marginal portions of the web are glued to one another to form the tube by means of an adhesive strip that is applied to the web. Usually, the shaping of the tube is performed in such a manner that the region of the tube which includes the longitudinal seam is situated at the upwardly facing portion of the tube from which one of the major panels of the bag is to be formed.
The separation of the individual tubular pieces for the formation of the bags is occasionally achieved in such a manner that the transversely extending end edges which are provided on the major panels of the bag extend at such a longitudinal offset from one another that the transverse end edge which is formed on the upper layer is offset rearwardly, as considered in the advancement direction, from the end edge that is formed on the lower layer of the tube and thus of the tubular piece formed therefrom. As a result of this, the lower layer of the respective tubular piece is connectable with the upper layer by folding-over of the leading end of the respective tubular piece. In addition, the edge portion which is provided on the upper layer of each of the tubular pieces at the trailing end thereof projects beyond the edge of the lower layer. Inasmuch as the trailing end eventually constitutes the filling opening of the bag, the projecting edge portions of the upper layer of the respective tubular pieces can also be considered as to constitute respective projecting flaps. The introduction of the goods or items into the bag is considerably facilitated by using this expedient. As far as the handling of the bags is concerned, the bag major panel which is provided with the longitudinal seam can be designated as the rear panel and the other major panel as the front panel.
The separation of the tube into the individual tubular pieces can be accomplished in various ways. So, for instance, the web may be provided prior to the shaping or deformation thereof into the tube with weakening lines which extend over the entire width of the web and which are so arranged that there is obtained the desired offset of the end edges after the tearing-off along these weakening lines. In accordance with another known method, the separation occurs with a so-called zigzag cut by means of sawtooth-shaped cutting blades or knives. The cutting blades may either by arranged stationarily, in which case the actual cut is accomplished by means of a knockover or backing-off element that rotates transversely to the transportation or advancement direction, or, in another construction, they may be mounted on rotating cylinders. In all of the known methods of separation of the tubular pieces from the tube, the projecting open end edges no longer satisfy, owing to the utilization of the zigzag cutting blades or the tearing-off along the weakening lines, the current requirements, especially since an advertising effect is to be achieved as well during the purchase of goods by the bags and their appearance.
A further disadvantage is to be seen in the fact that, especially when the separation is being achieved by the use of the rotating knockover element, the level of the noise generated by the machine is too high, so that the annoyance of the operating personnel by this noise is no longer acceptable, with the result that noise-damping measures become necessary.